The present invention relates to a toner composition for electrophotography, and more specifically, to a toner composition for electrophotography having melting properties upon heating suitable for fast reproduction and excellent carrier contamination resistance and image-forming properties.
With regard to machinery and tools such as copying apparatuses, printers and machines in which an electrophotography technique is employed, it has been strongly desired to suppress carrier contamination by toner particles and formation of fine particles due to the destruction of toner particles as much as possible for the purpose of obtaining images of high quality over a long period of time.
Conventionally, the binder resins most commonly used in toners have been vinylic polymers mainly comprising styrene. The styrenic resins per se are fragile and have low wear resistance. This causes so-called carrier contamination in which the toner particles or fine pieces thereof are adhered or welded onto the surface of carrier particles or a charging blade during a process for mixing the toner particles with the carrier particles or a friction process between the toner and the blade to thus contaminate the surface thereof. Hence the electrical properties of the resulting developer are deteriorated. This causes a reduction in image density. For the same reasons, in the case of one-component toners, are caused serious image defects. For instance, non-image portions are contaminated by fine toner particles generated due to the destruction thereof during mixing the toner particles.
One means for solving this problem is to increase the molecular weight of the binder resin to thus impart tough properties to the toner particles. However, this method causes an increase in the melt viscosity of the toner. As a result, the toner does not have sufficient flow properties during fast reproduction or during hot roll fixing at a relatively low temperature and pressure. Therefore, the permeation or adhesion of the toner to materials to which the toner is fixed becomes insufficient, which in turn leads to so-called insufficient fixing. More specifically, images are easily removed when the images are rubbed after the reproduction.
Another means for solving the foregoing problem is to cover the surface of carriers with a variety of resins to prevent the deterioration of a developer due to the contamination of the carrier. However, the effect of preventing the formation of fine toner particles cannot be expected by this method. Hence it is impossible to completely prevent the occurrence of image defects. Furthermore, this method cannot be applied to so-called one-component developers free of carrier particles.